1. Field of the Invention
The present invention relates to motion compensated de-interlacing in video signal processing, particularly recursive de-interlacing
2. Description of the Related Art
De-interlacing is performed when it is required to convert a video signal from an interlaced signal to a sequential or progressively scanned image signal. Additional lines need to be generated to insert between the signal lines of a field already supplied. This can be done by creating pixel values corresponding to the arithmetical mean, or the median, of positionally corresponding pixel values of two neighboring existing lines of the same field, or the interlaced line of the previous field may be taken into account. An improved image is obtained if a motion compensation interpolation is used. This compares lines in two adjacent fields to determine whether segments of missing lines are moving or not. If the segment is moving, a motion vector is generated and the segment is handled differently. Inaccuracies in the motion vector estimates lead to aliases and visible distortions.
A processing circuit is known in U.S. Pat. No. 5,532,750 for motion compensated de-interlacing of a radio signal, this processing circuit comprising a line memory, a de-interlacing circuit, a frame memory, and a cache memory to mix current and motion compensated previous data in a controlled manner.
In U.S. Pat. No. 5,657,401 a noise measurement circuit for video apparatus, using a plurality of noise estimates, is described.
However, this known processing circuit is affected by random or arbitrary motion vectors. Such vectors are particularly common in noisy images or those containing large homogeneous parts, and these vectors tend to cause or exaggerate fragmentation of objects, correlation of noise and undesirable error propagation. To counter these disadvantages, the level of de-interlacing is often reduced in practice, and thus, the vertical alias reduction is not as good as it should be.